The Multihash Data Format
draft-multiformats-multihash-00

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Network Working Group                                           J. Benet
Internet-Draft                                             Protocol Labs
Intended status: Standards Track                               M. Sporny
Expires: February 13, 2019                                Digital Bazaar
                                                         August 12, 2018

                       The Multihash Data Format
                    draft-multiformats-multihash-00

Abstract

   Cryptographic hash functions often have multiple output sizes and
   encodings.  This variability makes it difficult for applications to
   examine a series of bytes and determine which hash function produced
   them.  Multihash is a universal data format for encoding outputs from
   hash functions.  It is useful to write applications that can
   simultaneously support different hash function outputs as well as
   upgrade their use of hashes over time; Multihash is intended to
   address these needs.

Feedback

   This specification is a joint work product of Protocol Labs [1], the
   W3C Digital Verification Community Group [2], and the W3C Credentials
   Community Group [3].  Feedback related to this specification should
   logged in the issue tracker [4] or be sent to public-
   credentials@w3.org [5].  .

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on February 13, 2019.

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Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  The Multihash Fields  . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Multihash Core Data Types . . . . . . . . . . . . . . . .   3
       2.1.1.  unsigned variable integer . . . . . . . . . . . . . .   3
     2.2.  Multihash Fields  . . . . . . . . . . . . . . . . . . . .   4
       2.2.1.  Hash Function Type  . . . . . . . . . . . . . . . . .   4
       2.2.2.  Digest Length . . . . . . . . . . . . . . . . . . . .   4
       2.2.3.  Digest Value  . . . . . . . . . . . . . . . . . . . .   4
     2.3.  A Multihash Example . . . . . . . . . . . . . . . . . . .   5
   3.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     3.2.  Informative References  . . . . . . . . . . . . . . . . .   5
     3.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   Appendix A.  Security Considerations  . . . . . . . . . . . . . .   6
   Appendix B.  Test Values  . . . . . . . . . . . . . . . . . . . .   6
     B.1.  SHA-1 . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     B.2.  SHA-256 . . . . . . . . . . . . . . . . . . . . . . . . .   6
     B.3.  SHA-512/256 . . . . . . . . . . . . . . . . . . . . . . .   6
     B.4.  SHA-512 . . . . . . . . . . . . . . . . . . . . . . . . .   7
     B.5.  blake2b512  . . . . . . . . . . . . . . . . . . . . . . .   7
     B.6.  blake2b256  . . . . . . . . . . . . . . . . . . . . . . .   7
     B.7.  blake2s256  . . . . . . . . . . . . . . . . . . . . . . .   7
     B.8.  blake2s128  . . . . . . . . . . . . . . . . . . . . . . .   7
   Appendix C.  Acknowledgements . . . . . . . . . . . . . . . . . .   7
   Appendix D.  IANA Considerations  . . . . . . . . . . . . . . . .   7
     D.1.  The Multihash Algorithms Registry . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Multihash is particularly important in systems which depend on
   cryptographically secure hash functions.  Attacks may break the
   cryptographic properties of secure hash functions.  These
   cryptographic breaks are particularly painful in large tool

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